Radio receiving system



ay 26, 1936. R. E. MATHES 2,041,846

' RADIO RECEIVING SYSTEM I Filed Nov. 2, 1954 i #54 i 3 I I an i I flu 5 A I fiV/ffil/[fl/xfi'f ram/54w i Jl/fZ/F/ffi E 5 l I -QQQQQ5/ y 9/ r i E v 5 g l 61/? m/ l Mum/M I V V 0 057500 W INVENTOR ATTORNEY Patented May 26, 1936 UNITED STATES PATENT OFFICE aamo RECEIVING SYSTEM of Delaware Application November 2, 1934, Serial No. 751,133

6 Claims.

My present invention relates to the radio si naling art, and to generally improve radio reception is one object of my present invention.

More particularly, my present invention isdirected towards a super-heterodyne receivin system in which intermediate frequency energy is kept substantially constant in frequency despite relative variations in the transmitted signal frequency and the local oscillator frequency used for heterodyning purposes. Another object of my present invention is to provide an improved method and improved apparatus for maintaining this constancy of intermediate frequency. In accordance with my present invention, I carry out this object by frequency multiplying local oscillator energy to such a value that the beat between the frequency multiplied energy and. the received signal energy corresponds in frequency to the frequency of the local oscillator. The beat energy is made of relatively large amplitude and is used to lock the local oscillator in step therewith. Should there be any relative variation in frequency to cause a change in the absolute value of the intermediate frequency, the local oscillator is varied in such a way that the frequency multiplied output is changed in extent and direction as to cause the beat frequency to become the constant value desired.

Still another object of my present invention is to provide a constant beat frequency arrangement for a receiving system utilizing a plurality of separated antennae. Other purposes and advantages of my present invention will be selfevident as the further description thereof proceeds.

As required by law, my present invention is defined with particularity in the appended claims. However, it may best be understood as to its structural organization and mode of operation by referring to the accompanying drawing which illustrates in schematic wiring diagram form my present invention applied to a receiving system making use of a multiplicity of separated antennae.

In the embodiment of my invention shown in the accompanying drawing, two receivers R1 and R2 are in the same direction and some distance removed from the central office 0. O. and the receivers and central office are all connectedby the same cable line-or other tone channel facilities, which facilities can be made suitable to carrier frequency operation.

A local oscillator L0 is set up at the receiving station nearest the central oflice and is adjusted, for example, to a frequency one-sixteenth of that of the transmitter (not shown). The oscillator L0 is adjusted to give feeble oscillations only andfeeds a two stage combined frequency multiplier and amplifier FM! and FM2. The first stage FMI multiplies the oscillator frequency three times and the second stage multiplies the first five times, thus giving at Y a resultant frequency fifteen times that of the oscillator L0.

This resultant frequency is then of such value that when beat against the incoming signal frequency picked up upon antenna Al the beat frequency is the same as the local oscillator LO frequency. The receiving circuit includes an electron discharge tube 3 for transferring the heterodyned energy to an intermediate frequency amplifier IFA. The intermediate frequency is greatly amplified and part of this amplified frequency from the intermediate frequency amplifier IFA is fed from the output circuit 5 into the grid circuit GC of the local oscillator as shown. As stated, the local oscillations are quite feeble so that a fairly strong output from the amplifier IFA when fed to the grid of the oscillator will, through frequency attraction, hold the oscillator at the frequency of the amplified beat signal or if the oscillator frequency is not too greatly different, will force it into oscillation at that frequency.

Now, if the frequency of either the transmitter or the local oscillator LO should vary slightly or should drift, the intermediate frequency would change accordingly, but the oscillator frequency would be forced to follow it and would be changed as much as the original frequency change. This change would be multiplied fifteen times through the frequency multiplier and would change the local beating frequency fifteen times as much as the original frequency variation. This would produce a correction in the opposite direction of the intermediate frequency. Equilibrium would be reached with a net change in the intermediate frequency of only one-sixteenth of the actual frequency change of the transmitter or local oscillator and would, therefore, greatly diminish the effect of signal frequency variations or drift.

Another portion of the oscillator frequency energy is fed onto the cable line CLl to the farther distant receiving station. This station has a frequency multiplier F'M' similar to that at the first receiver. The frequency from the first station is here amplified and multiplied and used as the beating frequency to produce exactly the same intermediate signal frequency as at the first station. This intermediate is then returned via the cable line CLZto the first station where it is combined in combining tube CT with the same signal frequency produced there by receiver RI. -The combined signal is then amplified by line ampli fier LA and beat by an intermediate frequency os-a phase of the two signals, the frequencies. ofneces- ,7

sity being identical. I I

. .It is to be clearly understood that nay-present invention is notto be limited to thefrequency values indicated on the drawing 'norfto the ratios stated in the specification for these are given only I by way of example.

'Among the advantages which the foregoingsetup has are: (A) The arrangement decreases frequency variations or drift in theresultant au io signal'to a small fraction, h'er'one-sixteenth, of i the actual signal changes; (B) The arrangement provides a combining method which isstable in ceivers; and, (D) The arrangement gives control of the entire receiving system to one station once adjustment; (0) The system provides exactly the same frequency for combination from several rethedesired transmitter has been tuned in. This eliminates the necessity of continually matching or adjusting the signal at both receivers and makes for stability. I I 7 Moreover, my invention has other uses than the one described hereinabove. For example, under certain circumstances it would be highly desirable to beable to transmit a frequency by means of wire lines from one pointto another a mile or .two apart, which frequency willhave an absolute relationship to another higher frequency at the originating point. I For instance, such an. ar-

rangementcould be used for checking at the distaut point of the :actual frequency of a radio transmitter, and for the comparison of this frequency against a frequency standard located at the distant point. If the frequency of the transmitter is used directly there is apt to be serious difiiculty involved in transmitting this frequency such a distance due to the high attenuation of radio frequency when transmitted over wire transmission lines. If a lower frequency could be used the difficulties involved in trans- -mitting that frequency would be diminished in proportion to the lowering of the frequency. However, this is subject to the drawback that normally it is not possible to ascertain absolute relationship between the high frequency and the lower frequency to be transmitted to the distant point. The method outlined hereinabove could be directly applied to this case. Instead of a pick-up coil connected to an antenna system as shown, a pick-up coil should be provided which would be in inductive relation to one of the radio frequency power circuits of the transmitter to be measured.

The voltage induced by this pick-up coil would operate through the frequency stabilization system as previously outlined and the operator would merely have to tune the local oscillator and frequency multiplication stages until the oscillator is pulled into positive control of the frequency picked up from the transmitter. If a portion of this frequency is picked off by transmission line CL! and this frequency instead again hetero dyned to produce an audible'note which could be observed by the operator when tuningthe from the transmitter.

oscillator and frequency multiplication stages it would givea positive and rapid indication as to when the controlof the oscillator had been locked into step with the frequency pickedup.

It would be observed whether the audible frequency shifted sharply when this 'pick up coil circuit was opened or closed.

The pick-up coil. doesnot necessarily have to be applied to the final stages of; the transmitter,

plifienthe relation ofwhosefrequency to that but could be applied to the crystaloutput am-' of the 'output'frequency of the transmitteris definitely known. The relation of this crystal frequency to the heterodyned frequencyproduced by the frequency stabilization circuit also being known, when this frequency is transmitted to the i distant point and precisely measured the actual transmitter :could I be readily frequency of the determined.

Having thus desCribedmy invention, What I claim is: I I I I 1. The method of radio reception which includes picking up radio frequency energy, locally generating energy; frequency multiplying the locally generated energy to a value in frequency such that themultiplied frequency energy when "heter'odyned' with the picked up energy produces a beat equal in frequency to the frequency of the locallygenerated energy, heterodyning the picked up 'energy w'ith the frequency multiplied energy, and controlling the frequency of the locally generated energy inaccordance with the beat produced by the heterodyning process.

'2. The method 2 of radio reception which in- I eludes picking up radio frequency energy at a pluralityof separated points, locally generating energy, frequency multiplying the locally generatcd energy sothat when the frequency multi plied energy is'heterodyned with the picked up energy the resultant beat equals in value the fre-' quency of the locally generated energy, heterodyning the frequency multiplied energy with the picked up energy and utilizing the beat produced by the heterodyning process to control the frequency of the energy locally generated.

3. A radio-receiving system comprising an antenna, a local oscillation generator, a frequency multiplier for frequency multiplying the energy generated by said generator to a suitable'value i such that when the frequency multiplied energy is'heterodyned with the energy picked up by the antenna the resultant beat is of a value equal in frequency to the frequency of the local generator, and means for applying the beat energy derived from the heterodyning process to the local oscillator in such a way as to lock the local oscillator into step with the beat frequency energy.

4. In a receiving system, a plurality of separated antennae, a single local oscillation generator means for frequency multiplying oscillations generated by said generator to a value in frequency such that when the multiplied frequency is heterodyned with the energy picked up upon the antenna the resultant beat frequency energy equals in frequency value the frequency of the 10- cal oscillation generator, means for locking the local oscillator in step with the beat frequency energy so produced, and means for combining beat frequency energies derived from energies picked up upon each of said antennae. 5; In a receiving system, an intermediate frequency amplifier, a heterodyne detector adapted to receive modulated carrier frequency energy and to impress upon said amplifier waves of a beat frequency, an oscillator operable under control of energy from said amplifier to generate waves of said beat frequency, and means including a frequency multiplier network connecting said oscillator on the output side thereof with said heterodyne detector, thereby to provide a wave the frequency of which is maintained suitably difierent from the frequency of said carrier energy so that, when heterodyned therewith, the

resultant waves of beat frequency are held substantially constant.

6. A system in accordance with claim 5 and having a plurality of independent energy collectors in combination with a separate heterodyne detector and intermediate frequency amplifier for each collector, and a utilization circuit including a second detector having a plurality of control electrodes each adapted to be fed with energy from a respective one of said amplifiers.

RICHARD EUGENE MATHES. 

